1. Field of the Invention
The invention involves a heat exchanger for condensation laundry dryers.
2. Description of the Background Art
A heat exchanger for condensation laundry dryers is known from DE 198 38 525 A1. The construction is characterized by small material requirements in spite of a small film thickness of the heat exchanger plates, by a large degree of rigidity obtained by the struts or the spacers, and by a good heat elimination on the cooling air side.
The invention involves a further construction of this type of heat exchanger such that in a dimensioning of the stack of plates corresponding to the dimensions of the stack of plates of the known heat exchanger, an increase can be obtained, or, in spite of smaller dimensions of the stack of plates, an adequate or equivalent cooling output can be obtained.
In a heat exchanger of the invention, in which the humid air channel goes through the heat exchanger plates, the struts can be provided on one or on both sides of the heat exchanger plates, depending on whether the heat exchanger plates are to be oriented in the horizontal or vertical position.
In the vertical installation position, no condensate can collect in the struts when the struts are arranged on both sides, so that the strut wall portions of the pocket-like cooling lamella form cooling surfaces which ensure an intensive heat elimination.
In the horizontal installation position, the struts are provided oil the other hand, merely on the upper side of the plates, so that they remain free from condensate.
In another construction, in which the heat exchanger plates have the cooling air channel passing through them, the spacers provided on a plate portion form, on the other hand, pocket-like molded projections, which are open into a humid air channel located between the heat exchanger plates. They thus form at the same time cooling surfaces, which ensure effective heat elimination. Also in this case, both in the horizontal and in the vertical installation position, the pocket-like projections stay free from condensate.
For both heat exchanger constructions, the struts or spacers thus cause at the same time, along with a corresponding increase of the channel surfaces to be brushed over with cooling air, an effective air swirl.
The degree of effectiveness of the heat exchanger can be further improved considerably in that the humid air channel is constructed as a flat tube such that its pocket-like struts in a horizontal arrangement of heat exchanger plates functionally are merely molded onto the upper tube flat side. In this case, the lower plate side of a heat exchanger plate then rests on the struts projecting upwards from the heat exchanger plate lying beneath it, so that in spite of the lack of struts projecting downwards on the lower side of the plate between heat exchanger plates, cooling air channels are present and thus the prerequisites for an intensive heat elimination are created.
The length of the struts extending perpendicularly to the humid air channel can correspond approximately to the width of the humid air channel constructed as a flat-tube. However, a strut length, which merely corresponds to a fraction of the width of the flat tube is preferred, such that the struts are provided in the longitudinal direction of the flat tube functionally offset from each other by gaps.
In an additional embodiment of this heat exchanger construction, it can be advantageous to provide the struts directed at an angle to the blower stream direction of the cooling air at least over a range of the flat tube wall portion, and possibly in certain areas even compacted or in a symmetrical angled arrangement with each other over the entire flat tube wall portion.
By these measures, an optimal flow deflection and distribution, or optimal impingement of the cooling surface, can be obtained for the cooling air in the heat exchanger as a function of the given installation ratios in the condensation laundry dryers, where the flow ratios can be further improved in the cooling air channels by a slightly convex curvature of the strut longitudinal sides perpendicular to the flow direction of the humid air.
A reduced dimensioning of the heat exchanger plates with an equivalent cooling output is thus possible, as long as the upper and lower channel wall portion of the humid air channel are constructed corrugated perpendicularly to the flow direction of the humid air, and the wave curves of both tube wall portions preferably run parallel to each other.
The same effect can likewise be obtained in heat exchangers in the alternate embodiment, provided the upper and lower plate parts of its heat exchanger plates are constructed so that they are corrugated in parallel to each other in the flow direction of the cooling air, and in the process, the depth of the corrugation trough functionally corresponds to approximately half of the mutual separation distance of both plate parts.
In order to manufacture the heat exchanger plates or the films of the heat exchangers that form the heat exchanger plates, different materials are suitable, such as plastic or aluminum, as well as different manufacturing processes. If plastic film is used to manufacture the plates, then it is to be molded thermally, for example, so that two halves result, which each form a plate part independently from each other, and which are made to overlap with each other, and then are fused, adhered, or pressure-attached to each other to be air-tight on the opposite longitudinal sides.
In like manner, it is possible to make the plastic films that form the two plate parts out of one piece and to make the two plate parts overlap with each other by folds of the plastic film and then merely bond them together along the two longitudinal edge portions that cover each other by fusing, adhering, or pressure-attaching.
Finally a preferred manufacturing method can include forming heat exchanger plates in a blow molding tool from an extruded plastic tube.
In order to manufacture the plate parts out of plastic, acrylonitrile-utadiene-styrene copolymers (ABS) or polypropylene are especially suitable, where in order to obtain the desired cooling outputs or the heat capacity and stability required for this, a film thickness of between 0.15 mm and 0.50 mm, preferably 0.30 mm, has proven to be advantageous.
In the case of the use of aluminum film to manufacture the plate parts or the heat exchanger plates, a film thickness is recommended of between 0.14 mill and 0.20 mm, preferably 0.15 mm, where the plate parts made out of aluminum film are to be connected together in an air-tight manner along the two edge parts lying across from each other by mutually fusing, adhering, or pressure-attaching them together.